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Exercise & Illness. To exercise or not?

Exercise is good for you. We all know that. But what happens when you are ill or not feeling at your best? Should you continue to push through it, or should you rest?

Sometimes the body will decide for you. As I write this, I am at the end of some kind of super cold. Urgh, just the thought of exercise over the past few days was exhausting, and the mere act of getting myself from my bed to the bathroom felt like quite an achievement! In this instance, it's a no-brainer. I really had no choice, but how about in other scenarios when you're just not sure?

Your immune system is working hard to defend you against the bacteria, viruses, and germs that you encounter every day. There are 2 main parts to the immune system:

• The innate immune system is your first line of defence and develops when we are young. This includes physical barriers; skin / mucous membrane that lines the respiratory and gastrointestinal tracts / chemical barriers; stomach acid and protective white blood cells which attack, trap, and destroy harmful invaders.

• The adaptive immune system is acquired. It takes over when the innate system is overcome. The two systems work together to make antibodies, and this is what's meant when we talk about building immunity. The immune system recognises the invader, which means it can stop it more effectively. This is the basis for vaccinations: expose the body to a small amount of the pathogen and it will know what to do in the future. This is also why children get so many more bugs.

What's the lowdown on exercise and the immune system?

A tough workout where you are breathing hard, sweating, and feeling some discomfort triggers a stress response in the body. When we're healthy, the body can easily adapt, and it is this progressive adaptation that makes us fitter and stronger. But when we are unwell, the stress of a challenging workout can be too much for our immune system. Now, before you dive headfirst into the sofa, thinking you have permission to feed that cold and binge on Netflix, think again!!

Working out is very different from moving the body, and rest is not always best. There is, after all, a middle ground between a tough workout and sofa surfing!

Low to moderate intensity, nonstrenuous movement can actually help you feel better.

What is low to moderate intensity?

Your level of training is going to be different to the next person, so it's not a one-size-fits-all and I would urge you to listen to your body and let your level of perceived exertion be your guide.

• Walking
• Gentle jogging
• Biking
• Swimming
• Yoga
• Stretching
• T'ai Chi

To exercise or not?

Listen to your body, let your symptoms be your guide, and always use common sense. There's a difference between working out and low to moderate-intensity movement. If you've got something contagious, then exercise at home or outside to avoid spreading it around at the gym or in your exercise class. Just because you feel well enough for some gentle movement doesn't mean the rest of us want to catch it!

Avoid your heart rate being raised significantly, as your body is already working hard to fight off illness. And avoid the following:

• Heavy strength training
• Long endurance activities
• High intensity interval training
• Sprinting

Still not sure?

Above the neck? - OK to train

This is a rule you may have heard of and what I generally use myself. A cold with generalised symptoms of a runny nose, sore throat and feeling sneezy, with no fever or body aches and pains, is generally ok as long as the intensity is low to moderate.

Below the neck? - Rest

If you have any symptoms such as coughing, shortness of breath, or have an elevated heart rate, fatigue, or muscle/joint pain or weakness, then get some rest.

Vomiting/diarrhoea — Rest

Why would you want to do anything?! Rest up.

Sleep deprived — Rest

If you are sleep deprived, then your body is not able to function optimally, which puts you at an increased risk of illness and injury. Go for a gentle walk to feel energised, but taking a nap is going to improve your health more than hitting the gym.

Sleep and health are strongly related, with insufficient sleep increasing the risk of many health-related problems. Reduced immunity, decreased insulin sensitivity, high blood pressure, increased inflammation, imbalance of hormones, and an increased activation of the sympathetic nervous system; activating the fight or flight response, which affects inflammation, immune response, and metabolism. The importance of sleep for health

Coming back to training following illness?

If you have been forced to rest for over a week/ten days due to illness, then as frustrating as it may feel, you're going to need to build your training back up gradually.

Do not try to jump straight back in at the point that you stopped, as this is a sure fire way of overloading your body and putting yourself at risk of injury and further illness. Muscles remember, so in no time at all you'll be back to your previous level of training. Trust the process.

Other factors affecting your immune system

There are other elements that affect the immune system, and many of us are exposed to these on a daily basis. If you want to boost your immune system, then pay attention to the following:

Psychological stress - Work, relationships, money

Lifestyle - Diet, drugs

Sleep - Not enough or poor quality sleep

Age - Our innate immune response can break down as part of the ageing process

But on the plus side, our training age, in other words, our level of fitness, can go some way to counteracting the aging process. A high level of fitness is protective as it may limit the stress response to exercise.

In summary

• Listen to your body. Symptoms below the neck = rest.
• Consistent, moderate-intensity cardio and resistance training can strengthen the immune system over time.
• Prolonged vigorous exercise can make you more susceptible to illness. For this reason, it's not uncommon for runners to get ill after running a marathon.
• Short vigorous exercise doesn't have an immune-suppressing effect.
• A high level of fitness is protective as it may limit the stress response to exercise.